Interferon-gamma release assay as a diagnostic test for tuberculosis-associated uveitis

BACKGROUND: To study the use of interferon-gamma release assay (IFN-γ) (IGRAs) as a diagnostic test for tuberculosis (TB)-associated uveitis (TAU). DESIGN: Prospective cohort study. PARTICIPANTS: Consecutive new patients (n=162) with clinical ocular signs suggestive of TAU, seen >1 year period at a single tertiary center. METHODS: All subjects underwent investigations to rule out underlying disease, including T-SPOT.TB and tuberculin skin test (TST). Twenty-one subjects with underlying disease and three with interdeterminate T-SPOT.TB results were excluded. Those with T-SPOT.TB- or TST-positive results were referred to infectious diseases physician for evaluation. Anti-TB therapy (ATT) was prescribed if required. Patients' treatment response and recurrence were monitored for six months after completion of ATT, if given; or 1 year if no ATT was given. MAIN OUTCOME MEASURE: Diagnosis of TAU. RESULTS: Mean age of study cohort (n=138) was 46.8±15.3 years. Majority were Chinese (n=80, 58.0%) and female (n=75, 54.3%). TST was more sensitive than T-SPOT.TB (72.0% vs36.0%); but T-SPOT.TB was more specific (75.0% vs51.1%) for diagnosing TAU. Patients with either a T-SPOT.TB (1.44; 95% confidence intervals (CI), 0.86–2.42) or TST (1.47; 95% CI, 1.12–1.94)-positive result are more likely to have TAU. The accuracy of diagnosing TAU increases when both tests are used in combination (area under the receiver operator curve=0.665; 95% CI, 0.533–0.795). Patients with both tests positive are 2.16 (95% CI, 1.23–3.80) times more likely to have TAU. Negative T-SPOT.TB or TST results do not exclude TAU (negative likelihood ratios <1.0). CONCLUSIONS: We recommend using a combination of clinical signs, IGRA, and TST to diagnose TAU.